This invention relates to means for extracting energy from waves on the surface of a body of water, and relates particularly to improvements over the device and method disclosed in U.S. Pat. No. 4,441,316 to Moody.
In the Moody patent, a cup-shaped chamber is disposed, open end down, on the surface of a body of water on which surface waves occur. The chamber floats on the surface with the lower, open end of the chamber submerged. The chamber is normally filled with a column of water to a level equal to that of the surrounding water. As surface waves pass the container, the variations in water pressure caused by the passing waves induce oscillations in the height of the water column in the container. In the embodiment disclosed in FIG. 8 of the patent, a piston is disposed within the upper portion of the container and floats on the surface of the water column therein. The piston, including a piston rod which extends upwardly through the closed upper end of the container, is fixedly attached to a hydraulic pump. Accordingly, as the height of the water column varies within the container in response to passing waves, the piston within the container is caused to vertically oscillate for driving the hydraulic pump for pressurizing a hydraulic fluid which is used for driving an electrical generator for generating electrical energy.
The patent does not discuss how the container itself, aside from the movements of the water column therein, reacts to the passing waves. A problem, not discussed in the patent, is that, to the extent that the floating container bobs up and down in concert with the passing waves, thus reducing the depth changing effects of the waves, pressure variations at the bottom of the container are reduced resulting in a corresponding reduction in the amplitude of oscillations of the water column within the container. This reduces the amount of energy generated by the system.
A cup-shaped member similar to that disclosed in the Moody patent (the subject matter of which is incorporated herein by reference) is disposed, open end down, in completely (or, as described hereinafter, xe2x80x9ceffectivelyxe2x80x9d completely) submerged relation beneath and dependent from a float. A column of water extends into the submerged member which includes, between the upper surface of the water column and the member closed upper end, a compressible fluid, e.g., air. Preferably, the water column and the overlying fluid are separated by an impervious, movable barrier for preventing direct contact between the water and the overlying fluid while allowing changes in the height of the water column. The submerged member is rigidly connected, e.g., by a vertical rod extending upwardly from the upper end of the member, to an energy converter, e.g., a hydraulic pump-electrical generator arrangement as disclosed in the patent.
In use, the height of the water column within the submerged member oscillates in response to overpassing surface waves. In response to such oscillations, the buoyancy of the member is changed resulting in vertical oscillations of the member beneath the float. Such oscillating movements drive the energy converter.
In one embodiment, the float from which the submerged member is dependent is of sufficient size relative to the passing surface waves as to be relatively immovable in response to the waves. Accordingly, the amplitude of the movements of the submerged member relative to the float is determined essentially solely by the movements of the member.
In a second embodiment, the float is dimensioned for vertical movements which are essentially in phase with the passing waves. Such wave-induced movements of the float increase the amplitude of the relative movements between the float and the submerged member for increasing the energy conversion efficiency of the system. For example, with a cresting wave tending to lift the float, an upward force is applied by the float to, e.g., the casing of the hydraulic cylinder. Simultaneously, owing to the increased water pressure caused by the wave, a decreased buoyancy of the submerged member applies a downward force to, e.g., the piston of the hydraulic cylinder. Thus, movements of the float, in addition to movements of the submerged member, drive the hydraulic cylinder.
Because the phase relationship of the movements of the float and the submerged member are of particular importance in the above-described second embodiment, means are preferably employed for synchronizing the movements of the submerged member with that of the float. Known means, such as the phase controlling mechanisms disclosed in the Moody patent, can be used.
In still another embodiment, a portion of an xe2x80x9ceffectively completelyxe2x80x9d submerged member extends above the water surface for increasing the volume of the air chamber. This provides increased changes in buoyancy, for greater power output, with a relatively small increase in the mass of the system.